Embodiments of the inventive concepts described herein relate to radiation-tolerant 3-dimensional unit metal-oxide field-effect transistors (3D unit MOSFETs) and more particularly, relate to 3D unit MOSFETs having radiation-tolerant characteristics hardened against single event effects and total ionization dose effects.
Radiation is referred to the flow of energy emitted from atomic or molecular components when the atomic or molecular components are unstable at higher energy levels. The radiation is represented in the radiation form of an X-ray, a gamma ray, an alpha ray, a beta ray, neutrons, or protons. The radiations are classified into a particle form or an electromagnetic-wave form. The particle form is referred to as a particle radiation, and the electromagnetic-wave form is referred to as an electromagnetic-wave radiation.
Although the radiations are different from each other, the intensity of the radiation or the influence exerted on an object may be estimated, based on the basic concept of energy flow, depending on the size of an amount of transmitted energy or the size of an amount of absorbed energy. The radiation may be incident to produce ions, which is called “ionizing radiation”, and other radiations are called “non-ionizing radiations.” In particular, the ionizing radiation causes the damage to a unit MOSFET constituting an electronic part by ionizing atoms of a semiconductor material of the unit MOSFET. Accordingly, the normal operation of the electronic part is not ensured and temporarily or permanently damages.
The damage to a semiconductor device by the incidence of the radiation is mainly classified into a total ionization dose effect and a single event effect.
If the width of the oxide film of a transistor is 10 nm or more, and if the ionizing radiation is incident to a part having an electric field, holes are trapped at the interface between the oxide film and the silicon. More specifically, if the ionizing radiation is incident in the state that a voltage is applied to the gate, hole trapping is caused at an oxide film interface between a source and a drain and thus channel inversion occurs, thereby forming a leakage current path that current flows. The leakage current path formed by the ionizing radiation causes an abnormal operation of the unit MOSFET, which is called the total ionization dose effect.
FIG. 1 is a view illustrating the configuration of a planer MOSFET according to the related art. FIG. 2 is view illustrating the configuration of a FinFet which is one of a 3D unit MOSFET. FIG. 3 is a view illustrating the configuration of a gate-all-around MOSFET (GAA MOSFET) which is one of the 3D unit MOSFET.
The planer MOSFET of FIG. 1 includes a gate to control the operation of the transistor, and a source, a drain, and a body through which a current flows by the gate.
The 3D unit MOSFET of FIGS. 2A and 2B and FIGS. 3A and 3B is configured in the shape of surrounding three planes (in the case of the FinFET of FIGS. 2A and 2B) or four planes (in the case of the GAA MOSFET of FIGS. 3A and 3B) of the gate. The source and the drain of the 3D unit MOSFET are positioned at both sides of the gate. Accordingly, the current signal by the gate flows to the source and the drain similarly to the conventional planer MOSFET.
The unit MOSFET illustrated in FIGS. 1 to 3 is formed on a silicon substrate, and the source, the drain, and the body of each unit MOSFET includes PN junctions. For example, in the PN junction of the unit MOSFET, when forming a reverse bias that a positive voltage is applied to an N-type part and a negative voltage is applied to a P-type part, and when the ionizing radiation is incident, electron-hole pairs are produced and electrons and holes flow in a source-drain direction and a body direction by an electric field formed by the reverse bias.
In general, since a current pulse is higher than an equilibrium state of a built-in potential in the state that the reverse bias is applied to the PN junction, carriers may not move into an opposite region, and thus a current does not flow. In contrast, the current pulse, which is generated as the ionizing radiation is incident, affects a circuit including the unit MOSFET, thereby causing a problem of changing stored data. The phenomenon is called the single event effect. In particular, recently, as a process becomes smaller, a gate capacitance is reduced. Accordingly, the influence by the current pulse generated due to the single event effect is strongly represented.
The total ionization dose effect and the single event effect make it difficult to ensure the normal operation of the unit MOSFET under the radiation environment and make a circuit or a system, which includes the unit MOSFET, abnormally operating under the radiation environment.